| Socialism with Chinese characteristics has entered a new era,and China’s economic development has entered a new normal,shifting from a high-speed growth stage to a high-quality development stage.High-quality development has become a new requirement for the development of various undertakings in China.Green,energy-saving,low-carbon and environmental protection have become the new industry of the construction industry,and the green and low-carbonization of the construction industry has put forward higher requirements for concrete materials.The emergence of microporous concrete is to meet this requirement,as a non-load-bearing lightweight porous concrete,compressive strength,flexural strength,water absorption,flexibility,volume stability,thermal insulation and durability and other aspects of the potential can be explored.For this reason,this paper uses hybrid fiber reinforcement method to improve the strength mechanics and dry shrinkage properties of microporous concrete.By adjusting the admixture of glass fiber(referred to as GF)and polypropylene fiber(referred to as PPF),with the same raw materials and ratios,the microporous concrete of three capacities of 800,1000,1200 kg/m~3was used as the basic object,and the two fibers were admixed at 0,1.0,1.5,2.0,2.5 kg/m~3as well as GF and PPF volume ratios of 1:2,1:1,2:1 for compounding,to compare the effects of single and compounding of fibers on the mechanical and dry shrinkage properties of microporous concrete of different capacities.The results showed that:(1)Effect of fibers on the mechanical properties of microporous concrete.The effect of fiber type and admixture amount on the mechanical properties of mixed fiber-reinforced microporous concrete was analyzed by extreme difference analysis,and the effect of each factor on the early and late compressive strength and late flexural strength was derived.The compressive and flexural strengths of all the test groups were positively correlated with the increase of the capacity,and the growth of compressive strength was more obvious for PPF and GF at low capacity.The compounding of fibers can improve the flexural strength of microporous concrete,and the synergistic effect of both reaches the maximum when the volume ratio of GF and PPF is 1:2.With the increase of fiber admixture,except for PPF,the compressive strength increases first and then decreases,and all other fiber types show positive correlation with the increase of fiber admixture.For the flexural strength,the addition of fiber only increases the flexural strength,and increases with the increase of the doping amount.The addition of fibers does not cause sudden fracture of the test block,and can effectively play the role of reinforcement,crack resistance and toughening.The experimental study of the impact of the capacity and different fiber groups on the compressive strength was found to be linear by fitting the law with the formula y=kx+b;it was found to be well correlated by the correlation coefficient R~2.The experimental effects of fiber type and admixture on compressive strength were quadratically related with the equation y=ax~2+bx+c,which were found to be mostly well correlated by the correlation coefficient R~2.(2)After calculating the bending ratio,it is concluded that the bending ratio of D-2.5 group is the largest in 800 kg/m~3capacity;P-2.5 group is the largest in 1000kg/m~3capacity;B-2.0 group is the largest in 1200 kg/m~3capacity.The larger the folding ratio,the better the flexibility,the better the resistance to cracking performance.(3)The effect of fiber on the dry shrinkage properties of microporous concrete.The dry shrinkage rate decreases with the increase of microporous concrete capacity.The addition of fibers increases the dry shrinkage rate of low-volume microporous concrete,but with the increase in volume,the pores in the matrix become less,the pore water content is reduced,the tensile stress due to water loss resulting in shrinkage will be compensated by the addition of fibers,effectively inhibiting the dry shrinkage deformation of microporous concrete.Among them,fiber 1:1 compounding group is the optimal choice.The effect of fibers on the water loss rate of microporous concrete mass.With the increase of the capacitance its change law is consistent with the dry shrinkage performance.(4)From SEM analysis,it can be seen that GF plays the role of"skeleton"in microporous concrete,which supports the overall strength of microporous concrete;PPF plays the role of bonding and toughening,which increases the performance of microporous concrete through the stress transfer of fibers;the two fibers can complement each other through compounding,which improves the overall performance of microporous concrete.performance. |
